Thread by @swapnakpanda

Do you think it's peculiar?

parseInt(0.5); // => 0
parseInt(0.05); // => 0
parseInt(0.005); // => 0
parseInt(0.0005); // => 0
parseInt(0.00005); // => 0
parseInt(0.000005); // => 0
parseInt(0.0000005); // => 5

Here's why. A JavaScript 🧵

➊ What is parseInt?

parseInt is a function which

→ takes a "String" input
→ parses this input
→ returns the parsed "integer" value

➋ What if input is not a String?

If input is not a String, it's first converted to String and, then parsed.

➌ How numbers are converted to Strings?

In most cases they are converted as is.

0.5 ⇨ "0.5"
0.05 ⇨ "0.05"
0.005 ⇨ "0.005"
0.0005 ⇨ "0.0005"
0.00005 ⇨ "0.00005"
0.000005 ⇨ "0.000005"

➍ Where is the odd?

For very small and large numbers, the number is converted to its exponential representation while converting to a String.

⇥ 0.0000005 ⇨ "5e-7"
⇥ 999999999999999999999 (21 9's) ⇨ "1e+21"

➎ Now, let's join the dots

parseInt(0.0000005)
⇩
parseInt("5e-7")
⇩
5

➏ One more puzzle

Can you say what below will return?

⇥ parseInt(999999999999999999999)

⇨ 1

Ohh God!!! 😂

➐ Final Words

parseInt expects a String input. If input is not a String, it's converted first.

Always ensure to pass an appropriate String to get expected result. Passing some other type may result weird output.

End of 🧵

Are you interested in such threads? I am sharing those regularly on HTML, CSS, JavaScript and React.

To never miss any, Follow me ✅